Food safety issue is greatly related to the national economy and the people's livelihood. To solve the food safety issue, some potential food hazards including physical hazard, chemical hazard and microbial hazard should be greatly taken into consideration. The physical hazard can easily be monitored and prevented and the microbial hazard can be controlled during food processing. Besides, the chemical hazard such as pesticide residue and veterinary drug residue can be generally controlled by tracking back to the original source because these harmful residues are artificially added during the growth period of food materials. However, the most troublesome problem is caused by some chemical hazardous compounds (e.g. acrylamide), which are not generated from exotic environment but spontaneously from Swedish National Food formed during food processing.
In April 2002, Swedish scientist Margareta Törnqvist from Stockholm University firstly found the neurotoxin and potential carcinogen, i.e. acrylamide, in fried or baked potato and cereal-based food [Tareke, E. et al. Analysis of acrylamide, a carcinogen formed in heated foodstuffs. J. Agric. Food Chem., 2002, 50: 4998-5006]. This publication indicated that acrylamide found in high-temperature heated (>120° C.) carbohydrate-rich food greatly exceeds the safety standard and probably induces cancer, which led to wide scare at that time. Meanwhile, scientists Administration (SNFA) analyzed over 100 kinds of food under randomization and reported corresponding results in its official website. In May 2002, British Food Standards Agency (BFSA) reported similar results. Subsequently, government organizations taking charge of food safety from other countries including Norway, USA, Australia, New Zealand and Canada also reported the acrylamide content in various food. Thus, the finding from Swedish scientists was widely confirmed. Meanwhile, many international organizations and research institutes commenced studies into the formation mechanism, toxicology and risk assessment of acrylamide in food. In March 2005, the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) Joint Expert Committee announced in Geneva that certain food that contain the carcinogenic toxin acrylamide can greatly harm people's health and especially some western-style snacks contain a considerable amount of acrylamide. Acrylamide is an acknowledged neurotoxin and carcinogen [JIFSAN/NCFST Workshop “Acrylamide in food, scientific issues, uncertainties, and research strategies,” 28-30 Oct. 2002. Rosemont, USA]. Results of animal test showed that a long-term exposure of acrylamide may not only induce pathological change of nervous system but also lead to various carcinogenesis. Further study indicated that this chemical contaminant is not present in food materials but formed during food processing [Mottram, D. S., et al. Acrylamide is formed in the Maillard reaction. Nature, 2002, 419: 448-449; Stadler, R. H., et al. Acrylamide from Maillard reaction products. Nature, 2002, 419: 449-450].
Acrylamide, a white crystalline solid, can be dissolved in water, ethanol, methanol, dimethyl ether or acetone, but cannot be dissolved in non-polar solvents such as heptane and benzene. The α,β-unsaturated amino system of acrylamide is very easy to react with nucleophilic groups such as the hydrosulfide group of cysteine via Michael addition, which induces pathological changes via affecting normal functions of protein.
Governments in many countries have restrictive standards for the acrylamide content. For instance, the acrylamide content in drinking water should not exceed 0.5 μg/L. According to this standard, the acrylamide content in each kilogram of French fries should be less than 0.5 μg. However, the average content of acrylamide in French fries is actually about 1480 μg/g, which is 2690 times as the content in normal safety standard. Meanwhile, the acrylamide content in other heat-treated food such bakery bread and cookies also greatly exceeds the safety standard. In China, there are also some popular food which are made by similar heat processing methods compared to western-style snacks (heating temperature ≧120° C.). These popular foods include Chinese traditional breakfast food (e.g. fried bread sticks and clay oven rolls), imported snacks (e.g. fried snack noodles and cereal breakfast), drinks (e.g. coffee and cocoa) and non-staple foodstuffs (e.g. tobaccos and cigarettes). Unfortunately, few researches have focused on the analysis, control and risk assessment of acrylamide in China since acrylamide was found in heat-treated food in 2002.
Mechanism study on the formation of acrylamide demonstrated that acrylamide is generated from the Maillard reaction of free asparagine, and this mechanism is widely acknowledged now. Maillard reaction is a series of complicated chemical reactions between reducing sugars and the free amino groups of amino acids or proteins. It is also one of important pathways contributing to the flavor generation during heat processing. There are three main reaction stages in the Maillard reaction: (i) Schiff base with a “C═N” bond is formed by the reaction between the carbonyl of reducing sugar and the amino group of amino acid, and subsequently the Amadori or Heyns product is formed by the rearrangement of Schiff base. (ii) Flavor compounds and intermediates are generated from the Amadori or Heyns product via different degradation pathways. (iii) Brown products of Mailard reaction are finally formed.
The formation mechanism of acrylamide regarding the participation of asparagine in the Maillard reaction is called “asparagine pathway”. The beginning of asparagine pathway is the initial stage of Maillard reaction. There are two different reaction pathways that can both induce the formation of acrylamide when the Schiff base intermediate which is in dynamic balance with N-glycosyl amino acid is generated: (i) Strecker pathway, in which the Amadori product is formed via the Amadori rearrangement of Schiff base, carbonyl-containing products are subsequently formed via dehydration and deamination, acrylamide is finally formed via the Strecker degradation of asparagine and dehydration & deamination in the presence of carbonyl-containing products; (ii) N-glycoside pathway, in which oxazolidone is initially formed via undergoing the intramolecular cyclization of Schiff base, the decarboxylated Amadori product is subsequently formed and, acrylamide is finally generated via fragmentation of the “C—N” bond of decarboxylated Amadori product [Zhang, G. Y. Formation mechanism and risk assessments of acrylamide generated in heated foodstuffs. J. Wuxi Univ. Light Ind., 2003, 22(4): 91-99]. Yaylayan et al. and Becalski et al. (2003) further confirmed asparagine is a key precursor contributing to the formation of acrylamide [Yaylayan, V. A., et al. Why asparagine needs carbohydrates to generate acrylamide. J. Agric. Food Chem., 2003, 51: 1753-1757; Becalski, A., et al. Acrylamide in food: occurrence, sources, and modeling. J. Agric. Food Chem., 2003, 51: 802-808]. Elmore et al. (2003) also demonstrated the formation mechanism and precursors of acrylamide in potato, wheat and rye models [Elmore, J. S., et al. Measurement of acrylamide and its precursors in potato, wheat and rye model systems. J. Agric. Food Chem., 2003, 51: 4782-4787].
Based on the above mechanism, the formation of acrylamide during heat processing would have been reduced if the free asparagine in original food materials had been removed or the Maillard reaction had been inhibited. Current studies indicate that there are two ways for reduction or inhibition of the acrylamide formation during heat processing, i.e. (i) modification of heat processing conditions (e.g. heat processing styles, heating temperature and heating time) and (ii) modification of processing attributes of food materials. First, the formation of acrylamide is affected by the heat processing temperature, time and styles. Therefore, acrylamide can be reduced or inhibited by the control of these important heat processing conditions. For instance, (i) acrylamide can be reduced by a water-cooking method through the control of heating temperature (45-78° C.) and heating time (>4 min) [Lindsay, R. C. & Jang, S. Method for suppressing acrylamide formation. US patent, US2004/0224066 A1]. Acrylamide can be reduced by the control of frying and heating processes such as peeling, washing, par-frying and oil leaching [Barry, D. L. et al. Method for reducing acrylamide formation in heat processing food. PCT patent, WO2004/075656 A2], the mechanism of which is the inhibition of the lipid-glycerol-acrolein-acrylic acid-acrylamide pathway via the reduction of lipid pyrolysis degree [Tricoit, J. et al. Method for preventing acrylamide formation during heat treatment of food. US patent, US2004/0115321 A1; Tricoit, J. et al. Method for preventing acrylamide formation during heat-treatment of food. EU patent, 03292813.7]. Second, acrylamide can be reduced or inhibited by modifying or controlling processing attributes of food materials and adding other components. For instance, (i) acrylamide is greatly reduced by the addition of divalent or trivalent metal cations, which can come from food containing calcium, magnesium, copper, aluminum and iron salts [Elder, V. A. et al. Method for reducing acrylamide formation in heat processing food. PCT patent, WO 2004/075657 A2; Elder, V. A. et al. Method for reducing acrylamide formation in heat processing food. US patent, US 2004/0085045 A1]. (ii) Acrylamide can be reduced by a simple treatment with a pH-lowering agent, in which a nucleophilic amino group (—NH2) is protonated and converted into a non-nucleophilic amine (—NH3+) [Baardseth, P. et al. Reduction of acrylamide formation. PCT patent, WO 2004/028278 A2; Jung, M. Y. et al. Method for the reduction of acrylamide formation. PCT patent, WO 2004/060078 A1; Jung, M. Y. et al. A novel technique for limitation of acrylamide formation in fried and baked corn chips and in French fries. J. Food Sci., 2003, 68: 1287-1290]. (iii) Acrylamide can be reduced by the decrease of precursors thereof in food materials (including the use of microorganisms to metabolize sugars or the addition of asparaginase to convert asparagine into aspartic acid) [Awad, A. C. Reduction of acrylamide formation in cooked starchy food. US patent, US 2004/0086597 A1; Elder, V. A. et al. Method for reducing acrylamide formation in heat processing food. PCT patent, WO 2004/026042 A1]. (iv) Acrylamide can be reduced by the addition of at least one amino acids selected from the group consisting of cysteine, lysine, glycine, histidine, alanine, methionine, glutamic acid, aspartic acid, proline, phenylalanine, valine and arginine. These amino acids can also react with sugars and simultaneously inhibit the reaction between asparagine and reducing sugars because of the competitive inhibition principle [Elder, V. A. et al. Method for reducing acrylamide formation in heat processing food. PCT patent, WO 2004/075655 A2]. Although all of the above approaches may theoretically inhibit the generation of acrylamide, they are difficult to be applied in actual food processing when method practicability, organoleptic request of food and edible safety are taken into consideration. Therefore, it is still necessary to search novel approaches, which not only effectively reduce the acrylamide content, but also remain original flavor and texture of food. Recently, Chinese researchers used the Ca2+ and ferulic acid spiked asparagine-glucose simulated system to investigate the reduction of acrylamide. Results demonstrated that more than 80% of acrylamide was reduced within the optimal addition level of Ca2+ and ferulic acid and optimal reaction temperature and time [Ou, S. Y., et al. Acrylamide inhibitor used for heat processing food and its technical application method. CN patent, CN 1561866A]. However, there are significant differences of reduction effect between actual food system and simulated system. Therefore, this novel technique needs to be further investigated in actual food systems. Meanwhile, the variation of acrylamide content from “asparagine pathway” with the change of heat processing conditions should also be further investigated.
A PCT patent application filed by researchers from Food Technology Institute of Finland Helsinki University and published in 2004 discloses that addition of flavonoids could effectively reduce the acrylamide content in French fries. In their study, a flavonoid-enriched plant extract (0.05%-0.15%), consisting of green tea extract (45%), apple juice concentrate (45%) and onion juice concentrate (10%), was added during the frying process. Results indicated that about 50% of acrylamide was reduced during actual frying process of French fries [Kurppa, L. A process and composition for prevention of reducing the formation of acrylamide in food. PCT patent, WO 2004/032647 A1].
Flavonoids, a class of important functional factors in food, are widely present in medicinal herbs, vegetables and fruits. Flavonoids have great bio-antioxidant activity and strong protection effect against cardio-cerebral vascular diseases, cancer and diabetes. Currently, addition of plant flavonoids may be an appropriate method for the reduction of acrylamide formation in food because this method can ensure both food safety and food functionality simultaneously.
Many kinds of flavonoid-rich plant extracts such as tea extract, liquorice extract and rosemary extract are widely used for food antioxidants all over the world. The present inventors have recently developed a bamboo leaf extract, which is also called “antioxidant of bamboo leaves” (AOB). AOB has already been approved as a novel food antioxidant and listed in China Hygienic Standard for the Use of Food Additives (GB-2760) issued by China Ministry of Health in April 2004. As described above, AOB is a natural phenolic part extracted from bamboo leaves and includes flavonoids and phenolic acids as its major components. In detail, there are four bamboo-leaf C-glycosyl flavones (i.e. orientin, homoorientin, vitexin and isovitexin) and three phenolic acids (i.e. chlorogenic acid, ferulic acid and caffeic acid) in AOB [Zhang, Y., et al. Antioxidant of bamboo leaves and its applications. CN patent, CN 1528197A]. Their chemical structures are shown as follows:

The structural characteristic of bamboo-leaf C-glycosyl flavones is the C—C bond linkage between the flavone parent nucleus and glucosyl at C6 or C8 position in the flavone molecular. The C-glycosyl flavones have extremely stability because of their strong C—C bond energy. Furthermore, they cannot be hydrolyzed by acid, heat and enzyme. Their good hydrophilicity is in favor of the application in various food systems. Under such consideration, C-glycosyl flavones are much superior to O-glycosyl flavones, especially suitable for the use in heat processing food. Although studies on flavonoids started over 100 years ago, most of researches focused on flavone aglycones (e.g. quercetin) and O-glycosyl flavones (e.g. rutin). Studies on the structure and functionality of C-glycosyl flavones initiated since 1990s. Hitherto, studies on the effect of C-glycosyl flavones on the reduction of acrylamide in heat processing food have not ever been reported.
Considering the unique background of bamboo leaves (dual use of drugs and food) and their outstanding functionality, AOB will have a very bright application prospect in food industry.